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How To Resolve "Java compiler level does not match the version of the installed Java project facet." Issue in Eclipse, STS tool or Eclipse Based Tools

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                  I have faced this issue during the Java 7 upgrade from Java 6 into one of our application. You will face this issue suppose if your application or project built on lower versions of Java (in my case it is Java 1.6) and you are trying to upgrade it to the Higher versions of Java (in My case it is Java 1.7), then Eclipse will throw this error in the tool. You will face this error even after changing the compiler version from build path. To fix this issue Follow the Below Mentioned Steps. 1.  Open the ' Markers ' Tab at the bottom of the eclipse or STS tool beside the ' Properties ' Tab. (as shown in the below figure) 2. Right Click on the Error as mentioned in the below figure. in The context menu click on the ' Quick Fix ' item as shown below in the figure. 3. Select the correct Java Project Facet from the ' Quick Fix ' Window. and click on the ' Finish ' Button. 4.  After Clicking on '

Java Important Links

The Story of the Java Platform  http://java.sun.com/nav/whatis/storyofjava.html Java Technology—An Early History  http://java.sun.com/features/1998/05/birthday.html Java Community Process   http://java.sun.com/aboutJava/communityprocess/ J2SE Platform Documentation  http://java.sun.com/docs/index.html J2EE home page  http://java.sun.com/j2ee J2EE Blueprints  http://java.sun.com/j2ee/blueprints/index.html EJB home page  http://java.sun.com/products/ejb Servlets home page  http://www.java.sun.com/products/servlet JSP home page  http://www.java.sun.com/products/jsp JDBC home page  http://www.java.sun.com/products/jdbc JMS home page  http://www.java.sun.com/products/jms JNDI home page  http://java.sun.com/products/jndi Connector home page  http://java.sun.com/j2ee/connector

Java Performance Checklist

• Specify the required performance. Ensure performance objectives are clear. Specify target response times for as much of the system as possible. Specify all variations in benchmarks, including expected response ranges (e.g., 80%  of responses for X must fall within 3 seconds). Include benchmarks for the full range of scaling expected (e.g., low to high numbers  of users, data, files, file sizes, objects, etc.). Specify and use a benchmark suite based on real user behavior. This is particularly  important for multi-user benchmarks. Agree on all target times with users, customers, managers, etc., before tuning. • Make your benchmarks long enough: over five seconds is a good target. Use elapsed time (wall-clock time) for the primary time measurements. Ensure the benchmark harness does not interfere with the performance of the  application. Run benchmarks before starting tuning, and again after each tuning exercise. Take care that you are not measuring artificial s

Be-Aware of the Performance of the String Concatenation...

                  The string concatenation operator (+) is a convenient way to combine a few strings into one. It is fine for generating a single line of output or for constructing the string representation of a small, fixed-size object, but it does not scale. Using the string concatenation operator repeatedly to concatenate n strings requires time quadratic in n. It is an unfortunate consequence of the fact that strings are immutable. When two strings are concatenated, the contents of both are copied. For example, consider the following method that constructs a string representation of a billing statement by repeatedly concatenating a line for each item: // In-appropriate use of string concatenation - Hits Performance drastically! public String statement() {      String res = "";      for (int i = 0; i < numOfItems(); i++)       res += lineOfItem(i); // String concatenation       return res; }                   This method performs very slow if the number of